The portion of water main pipe that broke last week, resulting in a geyser that flooded dozens of homes and businesses east of downtown Montreal, was expected to last another decade, according to an analysis ordered by the city after the pipe’s last inspection in 2018.
Chantal Morissette, the city’s director of water services, said steel cables providing structure to the pipe’s cement casing had, at that point, been degrading at a rate of one or two per year, an industry standard.
But, somehow, that pace accelerated in the six years since 2018.
“We are looking for what caused the conduit to deteriorate more quickly,” Morissette told reporters Tuesday afternoon.
Morissette held a technical briefing and news conference Tuesday after media reports revealed that morning that the pipe had been given an “A” grade on inspection, based on open data the city provides on the state of its aqueduct system.
Morissette said she wanted to clarify that letter grades are only used to determine whether or not smaller pipes need replacing. In the case of larger conduits like the one that burst on Friday, Morissette explained that more thorough criteria are used to determine their state and when to invest in upgrading them.
2 pipe segments identified
There is a total of 4,200 kilometres of water main pipes in the city; 3,600 kilometres are smaller pipes while 790 kilometres are larger and considered major conduits. Friday’s pipe was one of them.
The pipe, whose water supply has been closed, extends roughly 2.6 kilometres along René-Lévesque Boulevard and was built in 1985. It is made up of 389 six-metre segments, explained Normand Hachey, an engineer with Montreal’s water department.
Two segments out of 389 were singled out in 2018 as needing further analysis — the one that broke last week, as well as another one near St-André Street. Each segment is made of roughly 510 steel cables encased within cement.
In 2018, 35 cables were broken in the segment that burst and 30 cables were broken in the other segment, which Morissette assured would be replaced before the conduit is put back into use.
The amount of drinking water that gushed into the streets of south-central Montreal on Friday, Aug. 16. could have filled 16 Olympic-size pools.
The analysis provided to the city by a specialized firm found the two segments could breach after 65 cables had corroded. At a rate of two cables corroding per year, that gave the pipe that burst an estimated 15 more years of use.
The pipe’s next scheduled inspection was due within weeks, when Friday it unleashed a fountain so strong it rose to nearly the height of the Jacques-Cartier Bridge standing nearby.
“It was really bad luck that this happened earlier,” said Maja Vodanovic, the city’s executive committee member in charge of water and the borough mayor of Lachine.
“Everything was within standards of practice,” Vodanovic said. She lauded the city’s water department for its “rigour and competence.”
Same material as Calgary water main break
The 2.6-kilometre water main is built of a series of materials called pre-stressed concrete cylinder pipe, known by its acronym PCCP, including concrete with steel wires. Often, an interior steel casing is installed to waterproof the inside of the pipe.
Morissette said there are 150 kilometres of such pipes in Montreal.
A water main that broke in Calgary earlier this summer, cutting off hundreds of homes’ water supply in the northwest part of the city, was built of the same materials.
“We know that pipes of that era, especially late 1970s, early 1980s, have seen some premature break,” said Rebecca Dziedzic, an assistant professor in Concordia University’s department of building, civil and environmental engineering.
“It’s not every single pipe of this era that is going to break and do this huge blowout. But it does require attention.”
Dziedzic said standards for these kinds of pipes were improved in the late 1980s.
She noted the City of Calgary implemented a type of continuous acoustic monitoring on other such pipes after the water main broke there.
“That might be a solution for the City of Montreal, too, especially in this area,” she said. “Usually when there’s one break, there can be a cascading effect.”
Hachey, of the city’s water department, said the city in fact has three calls for tender out for continuous acoustic monitoring of pipes. One was meant to be for the pipe that burst.